For Thomas Crahan, a car isn’t simply a metallic box resting on four wheels. It’s more like a musical instrument — a pipe organ, or a piano — and he and his team of engineers at Infiniti go to great lengths to make sure it can sing to its driver.

“We’ve coined the term ‘engine music,’” said Crahan, who is regional product manager for the Infiniti G35, Nissan’s sport luxury car.

“We are trying to create a very engaging driving experience, and also create an emotional appeal with our products. And when you look at that the emotional triggers that are in cars, sound is one of the big ones,” Crahan said.

Silence is golden, as the famous saying goes, and in an increasingly busy and stressful world, when more of us are turning to noise-canceling headphones, or meditative retreats for some peace and quiet, the automotive industry is betting more consumers are going to pay for more of it.

Crahan and his team of engineers are part of a growing trend among automakers to improve the sensory experience of driving. In the 2007 model of the Infiniti G35 due out in November, for example, they spent over two years redesigning 80 percent of the engine parts to increase stiffness and dampen engine noise. The car also has a dual-stage intake and dual exhaust to improve the engine’s “melody,” Crahan notes.

“It’s like a pipe on organ,” he said. “Acoustic engineers spend their time optimizing the harmonics through the length of the exhaust, or the intake length and volume, to create a luxurious sound,” he said. Switching to the image of playing a piano note, Crahan added: “What makes it a rich musical experience is the harmonics excited in other strings from the one note you play, and we have acoustic simulation software lets us try out different scenarios.”

There are clear benefits to offering car buyers a quieter, or more melodic cabin experience, particularly in the luxury market, notes Jack Nerad, market analyst at Kelley Blue Book, a resource for vehicle information. The trend toward quiet is driven by the growth in ultra-quiet, gas-electric engined hybrid vehicles, and also by a desire on the part of manufacturers to differentiate their product in a competitive automobile marketplace, Nerad said.

“Manufacturers want every edge and quiet is near the top of every consumer’s wish list,” he said. “When you look at what people want in their cars, not everyone wants a cushy ride and great handling. But across the board people favor silence; they consider it a major benefit. So that’s why we are seeing a lot of attention being paid to car noise management, especially on the luxury end. And like most things that start out in the luxury segment, it’s making its way quickly to lower-end vehicles.”

In the luxury vehicle segment, a car’s basic functions — comfort, style and power — are generally taken for granted, notes Crahan, and so the details matter more. Consumers are constantly looking for more refinement, he said, and so it depends on how you differentiate yourself.

“All manufacturers are getting more sophisticated at reducing noise,” said Crahan. “But not all of them want to create emotional vehicles; those that do worry about his stuff.

“You want to have people say, ‘I really want to dive this car today.’ It’s not just utilitarian,” he continued. “We all have memories of cars that give us that feeling and the goal is to deliver that feeling to our customers. When you are producing an emotional brand, you have to take the emotional cues from your customers very seriously.”

Other automobile manufactures have achieved success in tuning out the exterior sounds their vehicles make, while improving the interior sound quality notes Tom Appel, editor of ‘Consumer Guide: Automotive,’ a guide for car buyers.

In some cases, the sounds a car makes have become an important part of its character, he said. The sound a Range Rover makes when it accelerates — a “baritone-like burble” — is deliberately “programmed” into the car, he said. Other vehicles, like the Mercedes Benz S550, are “supremely quiet” inside, Appel added.

“But if you put your foot down there is a mechanical hum — it’s wonderful,” he said. “And there is just enough of a hum to let you know there is a lot of power there.”

Some manufacturers — like Kia and Buick — are also surrounding their cars with an aura of luxury and quality by drawing attention to their near-silent interiors, Appel added.

“This is quite a new metric to measure the quality of a vehicle; it used to be performance and fuel economy, and now it seems to be quiet. And as this is a quality that’s normally associated with a luxury vehicle. If you have positioned yourself as a car that is quiet you have gone some distance to position yourself as a high quality, luxurious brand,” he said.

Toyota’s Lexus brand has worked for years to perfect the interior quiet in its luxury vehicles, notes Paul Williamsen, Product Education Manager at the University of Toyota, a division of the Japanese automaker that trains the company’s dealers and associates.

Fifteen years ago, the first Lexus LS 400 was the quietest car you could buy, and since then Lexus has continued to make improvements, said Williamsen. The recently-unveiled 2008 LS 600h L hybrid luxury sedan is quieter still, thanks to its gas-electric engine. At low speeds, much of the power to drive the car comes from an ultra-quiet electric motor, which doesn’t use pistons and vales, and so is much quieter than a gas engines.

“So hybrid technology is a real boon for the luxury segment of car, which has as a strong buying motivator its interior quiet,” Williamsen said. “That’s not necessarily the case with sporty vehicles.”

Toyota is taking other steps to improve the sound inside its vehicles. These include improving carpet and roof padding to dampen road vibrations and noise from aerodynamic drag, adding extra layers of sound absorption in the windshield, updating engine fuel injectors and adding sound absorption to the exterior dashboard panel.

“This wasn’t something we would normally do on an entry-level Yaris, or a Scion that costs $11,000,” Crahan said. “But we do it now.”